1. Field of the Invention
The present invention relates to a belt that holds thereon a row of self-drilling screws or the like headed screws so as to successively carry them into a power-driven screw driver, wherein this driver continuously and efficiently operates to drive and fasten those screws one by one to a pair of articles overlying one another. Particularly, the invention relates to such a belt especially adapted to hold and carry those screws each having a seal ring juxtaposed to the head and protruding radially and outwardly of the head to thereby increase the effective diameter thereof.
2. Prior Art
Some screw-holding belts of this type are disclosed in the U.S. Pat. No. 4,059,034 and some other prior art references. For example, the Japanese Patent Laying-Open Gazette No. 8-189520 teaches a screw-holding belt having a row of screw receptors from which screws can readily slip off. As shown in FIG. 5, this belt comprises a belt body 1 that is made of a flexible synthetic resin such as a polyethylene. Cutouts 2 formed in and along each of lateral sides of that body 1 are arranged at regular intervals for driving the belt to intermittently advance. A row of screw-holding cylinders 3 as the principal parts of the receptors are formed longitudinally of the belt body and at the same pitch as the cutouts so that shanks 7 of headed screws 6 may be inserted in and held by those cylinders. Four apertures 4 each of a sector form are also formed in the body such that they extend radially and outwardly from each periphery of the screw-holding cylinder 3. The sector has a pointed top merging with the periphery and a bottom located remote therefrom. Each cylinder 3, the four apertures 4 and four skirts 5 each interposed between the adjacent two apertures thus constitute each screw receptor.
In use, the belt of the described structure and loaded with the headed screws 6 will be set at first on a screw striker installed in a power driver not shown in detail. While the belt is advancing intermittently by the pitch mentioned above, a driver bit 9 will push the headed screws 6 one by one out of the belt body 1 so as to force them into articles that are to be fastened together. When each of the headed screws 6 thus springs from the belt, its head 8 will cause the skirts 5 to bend themselves towards the cylinder 3 until the cylinder 3 is broken at its portions merging with the pointed tops of apertures 4. It is noted here that the bending resistance of the skirts 5 will generally be proportional to a distance `A` (see FIG. 5) between the adjacent aperture bottoms.
In most cases, flexible materials for forming the belt bodies 1 have been soft polyethylenes. Polyethylenes have been found to further soften when used in summer at hot construction sites to such an extent that those belts could scarcely be driven by a correct predetermined pitch. Thus in some cases, harder polypropylenes have recently been substituting for polyethylenes as the materials of the screw-holding belts.
However, such hard polypropylene belt bodies 1 have often been observed to render the skirts 5 in the prior art structures more resistant to bend. Operators must apply a stronger power to the screw heads 8 at the step of removing same from the belt bodies, thereby causing a hard work to them. In addition, such a strong force have often caused deformation of those belt bodies 1, with the latter consequently failing to smoothly advance by a correct pitch. If those screw heads 8 had seal rings protruding outwards and radially therefrom, then those heads could not easily be thrust out even where the belt bodies 1 were made of a softer material.